I fixed it. ASC registry cleaner deleted some keys related to Windows Readyboost for Windows 7. I just use the built-in registry restore function with "Advance SystemCare". I think I won't use ASC registry cleaner from now on.
I heard the Readyboost in Windows 7 is a better version of Readyboost which is slightly faster then the version in Vista. But, Vista is slower then 7, so it could be the same.
The Vista and 7 readyboost both cache files on your Flash drive for faster access times.
However, RAM and the L1, L2, L3 Cache on your CPU are way faster,
Make sure your flash drive is fast enough for Windows 7, and if it is not buy a flash drive base on its max read and write speed and not base on "Readyboost compatible" drive since some slower flash drives can be used as Readyboost drives, but Readyboost works best on "faster" flash drives which has a write and read speed which is 20 MBps - 30MBps I read online.